I run 16 Lb. cap, each Lb. of pressure increases boiling point by 3 degrees F. With 16 lbs you're near 260 degrees for a boiling point. Once the coolant boils, it's all downhill as far as recovering without shutting down, cooling down, and adding more coolant.
Steam inside the system compromises cooling to the extent that you'll have to shut it off. No steam internally, and no coolant loss makes much better chances for a recovery without shutdown.
One other advantage is, the higher the pressure the less room for steam pockets throughout the system, making for more coolant contact with hot metal, and heat transfer is improved.
